District-heating line

Abstract

A district heating line comprising an inner metal tube intended for the transfer of a heating medium and encircled by an insulating layer of foamed plastic. Arranged around the insulating layer is a moisture impenetrable protective tube. To enable an alarm to be given in the event of a fault in the line, elongated blocks are fixedly mounted on the outer cylindrical surface of the metal tube. The blocks are made of electrically insulating material. They each have at least one radially extending, outwardly opening channel on the outer surface thereof with the channels on adjacent blocks aligned with one another. The channels are dimensioned to accommodate the electrical conductor and position it at a fixed distance from the outer cylindrical surface of the inner metal tube. The conductor is secured in the aligned channels at the fixed distance from the outer cylindrical surface of the inner metal tube. A water soluble salt is incorporated in the electrically insulating blocks.

We claim: 
     
       1. A district heating line of the kind including an inner metal tube for transporting a heat transfer medium, an insulating layer of foamed-plastic material arranged around the metal tube, a moisture impenetrable protective tube surrounding said foamed-plastic layer, at least one electrical conductor formed as part of an electrical circuit, elongated blocks mounted on and affixed to the inner metal tube along the length of the tube, said blocks being made of electrically insulating material and having extending along the length thereof at least one radially outwardly opening channel with the channels on adjacent blocks aligned with one another, said channels being dimensioned to accommodate said electrical conductor and position it at a fixed distance from the outer cylindrical surface of the inner metal tube, means securing said electrical conductor in said channels at said fixed distance from the outer cylindrical surface of the inner metal tube, and a water soluble salt incorporated in said electrically insulating blocks.